diff options
Diffstat (limited to 'kernel/rcu/tasks.h')
| -rw-r--r-- | kernel/rcu/tasks.h | 58 |
1 files changed, 51 insertions, 7 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 350ebf5051f9..03a118d1c003 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -23,7 +23,7 @@ typedef void (*postgp_func_t)(struct rcu_tasks *rtp); * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism. * @cbs_head: Head of callback list. * @cbs_tail: Tail pointer for callback list. - * @cbs_wq: Wait queue allowning new callback to get kthread's attention. + * @cbs_wq: Wait queue allowing new callback to get kthread's attention. * @cbs_lock: Lock protecting callback list. * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. * @gp_func: This flavor's grace-period-wait function. @@ -377,6 +377,46 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) // Finally, this implementation does not support high call_rcu_tasks() // rates from multiple CPUs. If this is required, per-CPU callback lists // will be needed. +// +// The implementation uses rcu_tasks_wait_gp(), which relies on function +// pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread() +// function sets these function pointers up so that rcu_tasks_wait_gp() +// invokes these functions in this order: +// +// rcu_tasks_pregp_step(): +// Invokes synchronize_rcu() in order to wait for all in-flight +// t->on_rq and t->nvcsw transitions to complete. This works because +// all such transitions are carried out with interrupts disabled. +// rcu_tasks_pertask(), invoked on every non-idle task: +// For every runnable non-idle task other than the current one, use +// get_task_struct() to pin down that task, snapshot that task's +// number of voluntary context switches, and add that task to the +// holdout list. +// rcu_tasks_postscan(): +// Invoke synchronize_srcu() to ensure that all tasks that were +// in the process of exiting (and which thus might not know to +// synchronize with this RCU Tasks grace period) have completed +// exiting. +// check_all_holdout_tasks(), repeatedly until holdout list is empty: +// Scans the holdout list, attempting to identify a quiescent state +// for each task on the list. If there is a quiescent state, the +// corresponding task is removed from the holdout list. +// rcu_tasks_postgp(): +// Invokes synchronize_rcu() in order to ensure that all prior +// t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks +// to have happened before the end of this RCU Tasks grace period. +// Again, this works because all such transitions are carried out +// with interrupts disabled. +// +// For each exiting task, the exit_tasks_rcu_start() and +// exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU +// read-side critical sections waited for by rcu_tasks_postscan(). +// +// Pre-grace-period update-side code is ordered before the grace via the +// ->cbs_lock and the smp_mb__after_spinlock(). Pre-grace-period read-side +// code is ordered before the grace period via synchronize_rcu() call +// in rcu_tasks_pregp_step() and by the scheduler's locks and interrupt +// disabling. /* Pre-grace-period preparation. */ static void rcu_tasks_pregp_step(void) @@ -504,7 +544,7 @@ DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks"); * or transition to usermode execution. As such, there are no read-side * primitives analogous to rcu_read_lock() and rcu_read_unlock() because * this primitive is intended to determine that all tasks have passed - * through a safe state, not so much for data-strcuture synchronization. + * through a safe state, not so much for data-structure synchronization. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. @@ -605,8 +645,13 @@ void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); } // passing an empty function to schedule_on_each_cpu(). This approach // provides an asynchronous call_rcu_tasks_rude() API and batching // of concurrent calls to the synchronous synchronize_rcu_rude() API. -// This sends IPIs far and wide and induces otherwise unnecessary context -// switches on all online CPUs, whether idle or not. +// This invokes schedule_on_each_cpu() in order to send IPIs far and wide +// and induces otherwise unnecessary context switches on all online CPUs, +// whether idle or not. +// +// Callback handling is provided by the rcu_tasks_kthread() function. +// +// Ordering is provided by the scheduler's context-switch code. // Empty function to allow workqueues to force a context switch. static void rcu_tasks_be_rude(struct work_struct *work) @@ -637,7 +682,7 @@ DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude, * there are no read-side primitives analogous to rcu_read_lock() and * rcu_read_unlock() because this primitive is intended to determine * that all tasks have passed through a safe state, not so much for - * data-strcuture synchronization. + * data-structure synchronization. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. @@ -1163,7 +1208,7 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t) * there are no read-side primitives analogous to rcu_read_lock() and * rcu_read_unlock() because this primitive is intended to determine * that all tasks have passed through a safe state, not so much for - * data-strcuture synchronization. + * data-structure synchronization. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. @@ -1356,5 +1401,4 @@ void __init rcu_init_tasks_generic(void) #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ static inline void rcu_tasks_bootup_oddness(void) {} -void show_rcu_tasks_gp_kthreads(void) {} #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ |